Fluorine implantation effect on boron diffusion in Si

Boron diffusion was studied in the BF2+ implanted Si by secondary ion mass spectroscopy. Anomalous boron diffusion was observed in the excess Si region of the amorphized layer at low temperatures below 300 °C. This was explained by a diffusion model where boron was assumed to diffuse by way of an intermediate species BI formed of interstitial Si(SiI) and substitutional boron. It is also found that fluorine plays a significant role in enhancing boron diffusion even at an annealing temperature as low as 300 °C, although the enhanced boron diffusion was reported only to occur at annealing temperatures above 600 °C. Fluorine may hinder SiI from growing into large clusters which need a high temperature annealing to dissociate into freely migrating species. Exponential diffusion profile of fluorine could be explained by a model of SiI–F complex formation. This complex consumes SiI resulting from small Si clusters which could dissociate at low annealing temperatures. This result also supports that boron diffusion at high annealing temperatures may be suppressed by co-implantation of fluorine.